Discrete Sensors in OpenBMC

Discrete Sensors in OpenBMC

[Wludzik, Jozef]

Does anyone use or implement discrete sensor in OpenBMC? Redfish defines 
discrete triggers that use discrete values to detect that threshold is 
crossed and trigger action should be commited. Redfish does not mention 
about discrete sensor/values in other topics/schemes than Telemetry 
(e.g. MetricDefinition, MetricReportDefinition and MetricReport). I am 
asking about it because we are trying to find an example of discrete 
sensor to proceed with DiscreteTriggers implementation (aka Discrete 
thresholds) from Triggers scheme.

Ref.:

Redfish Telemetry White Paper - 
https://www.dmtf.org/sites/default/files/standards/documents/DSP2051_1.0.0.pdf

Thanks,
Jozef

Re: Discrete Sensors in OpenBMC

[Patrick Williams]

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On Tue, Jan 19, 2021 at 03:22:41PM +0100, Wludzik, Jozef wrote:
> Does anyone use or implement discrete sensor in OpenBMC? Redfish defines 
> discrete triggers that use discrete values to detect that threshold is 
> crossed and trigger action should be commited. Redfish does not mention 
> about discrete sensor/values in other topics/schemes than Telemetry 
> (e.g. MetricDefinition, MetricReportDefinition and MetricReport). I am 
> asking about it because we are trying to find an example of discrete 
> sensor to proceed with DiscreteTriggers implementation (aka Discrete 
> thresholds) from Triggers scheme.
> 
> Ref.:
> 
> Redfish Telemetry White Paper - 
> https://www.dmtf.org/sites/default/files/standards/documents/DSP2051_1.0.0.pdf
> 
> Thanks,
> Jozef
> 

My impression is that IPMI called a lot of things "sensors" which were
not really hardware sensors and they often became a discrete sensor.  So
far we haven't had any real hardware sensors that are discrete.  All of
the Sensor definitions are in phosphor-dbus-interfaces[1].

There seems to be a bit of a throwback to IPMI terminology here though
with Redfish Telemetry.  For telemetry it could be very useful to keep
track of things which are indeed discrete (but not really a "sensor").
For example, log-in attempts might be something useful to insert into
telemetry but have a discrete component ("successful", "failed").  For
cases like this, we wouldn't have them under the Sensors namespace in
dbus but whereever is relevant to their domain.  I think you could find
a lot of data out in various namespaces which might be interesting to
place into telemetry but are not "sensors".

1. https://github.com/openbmc/phosphor-dbus-interfaces/tree/master/xyz/openbmc_project/Sensor

-- 
Patrick Williams

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Re: Discrete Sensors in OpenBMC

[Ed Tanous]

On Tue, Jan 19, 2021 at 6:23 AM Wludzik, Jozef
<jozef.wludzik@linux.intel.com> wrote:
>
> Does anyone use or implement discrete sensor in OpenBMC? Redfish defines
> discrete triggers that use discrete values to detect that threshold is
> crossed and trigger action should be commited. Redfish does not mention
> about discrete sensor/values in other topics/schemes than Telemetry
> (e.g. MetricDefinition, MetricReportDefinition and MetricReport). I am
> asking about it because we are trying to find an example of discrete
> sensor to proceed with DiscreteTriggers implementation (aka Discrete
> thresholds) from Triggers scheme.

A "discrete" sensor is terminology that's only used in IPMI.  The
equivalent in Redfish would be an enum type property, of which there
are many examples.  The most obvious discrete-like sensor that we have
an example of today would be the Systems PowerState parameter, which
changes state based on the power state of the system.

If you're looking to stream events through redfish, generally you
would implement some kind of property, then you would implement a
Resource Changed event that someone could subscribe to from here:
https://redfish.dmtf.org/registries/ResourceEvent.1.0.3.json

We don't have the subscription part implemented yet, but there was
some talk about getting that going.

>
> Ref.:
>
> Redfish Telemetry White Paper -
> https://www.dmtf.org/sites/default/files/standards/documents/DSP2051_1.0.0.pdf
>
> Thanks,
> Jozef
>

Re: Discrete Sensors in OpenBMC

[Wludzik, Jozef]

Thanks for responses. It sounds reasonable. As initial implementation
discrete threshold/trigger will allow to monitor sensor without
differentiate between type of sensor (e.g. thermal, power, voltage,
...). If anyone will require additional type of resource to be monitored
by Telemetry (e.g. intrinsic sensor to check if chassis is closed), than
it is possible to extend the implementation.

I liked the idea to stream resource events. It seems that it is the same
as discrete threshold but threshold allows to commit an action on
specific value of a resource/sensor. One of the trigger actions is
logging a Redfish Message that can be streamed as Event.

Thanks,
Jozef

On 1/21/2021 17:46 PM, Ed Tanous wrote:
> On Tue, Jan 19, 2021 at 6:23 AM Wludzik, Jozef
> <jozef.wludzik@linux.intel.com> wrote:
>>
>> Does anyone use or implement discrete sensor in OpenBMC? Redfish defines
>> discrete triggers that use discrete values to detect that threshold is
>> crossed and trigger action should be commited. Redfish does not mention
>> about discrete sensor/values in other topics/schemes than Telemetry
>> (e.g. MetricDefinition, MetricReportDefinition and MetricReport). I am
>> asking about it because we are trying to find an example of discrete
>> sensor to proceed with DiscreteTriggers implementation (aka Discrete
>> thresholds) from Triggers scheme.
> 
> A "discrete" sensor is terminology that's only used in IPMI.  The
> equivalent in Redfish would be an enum type property, of which there
> are many examples.  The most obvious discrete-like sensor that we have
> an example of today would be the Systems PowerState parameter, which
> changes state based on the power state of the system.
> 
> If you're looking to stream events through redfish, generally you
> would implement some kind of property, then you would implement a
> Resource Changed event that someone could subscribe to from here:
> https://redfish.dmtf.org/registries/ResourceEvent.1.0.3.json
> 
> We don't have the subscription part implemented yet, but there was
> some talk about getting that going.
> 
>>
>> Ref.:
>>
>> Redfish Telemetry White Paper -
>> https://www.dmtf.org/sites/default/files/standards/documents/DSP2051_1.0.0.pdf
>>
>> Thanks,
>> Jozef
>>